Firstly this property belonged to your mother hence upon her intestate death this property shall devolve equally on all her legal heirs i.e., your father, your brother and yourself.
If you want this property to be on your name alone then the other two legal heirs have to transfer this proeprty to your name by executing a registered release deed relinquishing their rights in the property.
The question is not about their mental status of slow learning.
Until and unless they are declared as mentally insane people, they can still be considered as eligible to transfer their share in the property to your name.
It cannot be done on a Rs. 100 stamp paper, it has to be done by a registered deed alone.
There is no problem in you holding more than one house.
There are no tax implications on owing more than one house
You may have to show the income derived from the properties in your income tax returns, which will suffice all other requirements in this regard.